This invention relates generally to lawn and garden tractors and, more particularly, to control linkages for hydrostatic transmissions in such lawn and garden tractors.
Hydrostatic or hydraulic transmissions are used to advantage in lawn and garden tractors. Such transmissions are reliable, economical, durable and require little maintenance. Furthermore, in contrast to conventional transmissions that provide a limited number of fixed gear ratios, hydrostatic transmissions provide an infinitely variable speed range. This capability avoids the need to shift gears and simplifies vehicle operation. In addition, the continuous range of available speeds allows the operator to operate the vehicle at an optimum speed under all conditions of load.
Typically, hydrostatic transmissions include a rotatable control input shaft that governs how fast, and in what direction, the transmission operates. The resulting vehicle speed and direction of travel is determined by the rotational position of the control input shaft.
In contrast to conventional transmissions having gears that can be disengaged in a positive manner, hydrostatic transmissions vary hydraulic flow rates to obtain infinitely variable speeds. Accordingly, hydrostatic transmissions cannot be disengaged or placed in "neutral" in the same manner that a geared transmission can. Rather, "neutral" in a hydrostatic transmission corresponds to that setting of the control input shaft that balances the hydraulic fluid flow rates and results in no vehicle movement in either direction. The "neutral" setting in a hydrostatic transmission thus corresponds to a precise setting that frequently has very little "width" or tolerance. Accordingly, it is common for vehicles equipped with hydrostatic transmissions to move slowly or "creep" in one direction or another even though the vehicle has been placed in "neutral".
One possible source of vehicle creep is backlash in the control linkage that links the transmission control input shaft with a user-operated transmission control lever that typically is located adjacent the driver's position. Even though the operator places the control lever in a position marked "neutral", backlash in the linkage allows the transmission control input shaft to deviate slightly from the true "neutral" position. Vehicle creep is the result.
In view of the foregoing, it is a general object of the present invention to provide a new and improved control linkage for hydrostatic transmissions.
It is a further object of the present invention to provide a new and improved control linkage for hydrostatic transmissions that avoids vehicle creep when the vehicle is in "neutral".
It is a still further object of the present invention to provide a control linkage that minimizes or avoids the difficulties associated with backlash in the linkage system.